Labor saving techniques are essential given the current pressure on clinical cost containment. Since blood classification and screening is a notoriously labor intensive area of the clinical laboratory, manufacturers have concentrated on developing various ABO/Rh typing techniques. Few of us recognize the specialization needed in performing such tests, and the minor impact these tests have had in the blood transfusion laboratory. On the other hand, new techniques in immunology and hematology such as sensitive and objective "high-end" flow cytometry has replaced visual observation but remains too complex and costly for use by blood bankers. Yet, there is no tool available to do these types of measurements any differently, better or less expensively. In this proposal we describe a method suitable for both the blood bank and immunohematology laboratory. The technique can potentially combine red blood cell typing and lymphocyte subset analysis in a simple flow cytometry instrument. This approach can overcome the problem of background fluorescence interference. This is done using optical phase measurements of particle dry mass using a two-frequency HeNe laser source in an interferometric configuration. Measurement sensitivity is enhanced by the use of microbeads specific to cell membranes.